Here's a quick comparison and consider that I've only had the 6682 one day.
6682 - I think you'll find pretty quickly that it has an internal memory issue and be searching these forums for the answer to the problem. The answer is -it doesn't have enough internal memory and you'll need to close out open applications in order to take a picture even when it appears to have plenty of space and you're storing everything on the mmc. I found this problem after buying the phone... so much for my research ability.
The 6682 feels much more phone like when you put it against your head to make a call. The SDA didn't have that feel and I normaly searched for the sweet spot where the audio came through on the device.
On the RF side, the Nokia appears to be better. I'm in a 1 bar area and the SDA would drop calls and break up, so far the 6682 has been more stable but time will tell.
The overall feel of the keys, joystick and phone are better on the nokia although the camera cover does feel cheap and a litte sloppy. It's pretty typical nokia plastic.
I prefer the email app in the nokia series 60 over the SDA. There are two reasons but its still a little early to tell. One reason is that I can tell the phone what hours I want it to retrieve the email and with the SDA I had to change the profile each night. I never looked into add on apps or whether there was a solution to the SDA email retrieval hours. I also prefer the format of the email in the Nokia over the SDA but they are close.
Web browsing seems faster on the Nokia but I need to figure out how to save a password.. so far its making me re-enter it each time. The SDA seemed to save it automatically until I cleared the cache.
I think the battery life will be better with the Nokia.
That's it for now... I might come back and edit when I get more time.
I'm already thinking about my next phone.